Potassium Bromide, KBr, Crystallizes Like NaCl in a Face-Centered Lattice

Multiple Choice

Potassium bromide, KBr, crystallizes like NaCl in a face-centered lattice. The ionic radii of K⁺ and Br^- ions are 133 pm and 195 pm, respectively. Assuming that all Br^- ions are positioned in the face and corners of the unit cell, while the K⁺ ions are positioned along the edge alternating between anions, calculate the length of a unit cell edge.

A) 230 pm
B) 328 pm
C) 523 pm
D) 656 pm
E) 780 pm